The problem of the day.

You have four identical spheres (oranges in my case that represent ions) and they are stacked in a tetrahedral shape. That is, a pyramid with a triangle bottom. That is, three oranges placed together in a triangle with another orange placed on top of the triangle. In between the four oranges there is a space. In terms of the radius of the larger spheres, what is the radius of the largest sphere you can place in this space?

If I solve this and show how I did it, I don’t have to turn in my lab report for materials. I’ll let you know if and when I do.